Electric motors are a major consumer of energy but some types are relatively inefficient. The induction motor, the most common type of AC motor, has been around for over a century. They are provided in many sizes and power levels and are still widely used in many industries. However, their outdated design limits their efficiency.
The Electrically Commutated (EC) motor is an alternative solution proving to be a major source of energy savings, which is gaining popularity in many fields and applications. EC motors usually provide energy savings and allow reductions of size, weight and noise when integrated into a system such as an exhaust fan. These motors are increasingly available in various sizes and power outputs. An EC motor can make products simpler and smarter by allowing added features, more reliability and better performance.
There are some design differences between an Alternating Current (AC) induction motor and an EC motor. Although used in many types of applications, the operation of AC induction motors is fairly simple. AC power is supplied to the stator creating a magnetic field. The magnetic field rotates at the frequency of the AC voltage supplied, inducing an opposing current in the rotor. The rotor then responds by turning in an opposed direction to the rotating magnetic field. The speed of such a motor is dependent on the frequency of the input voltage and the number of poles in the motor, but cannot be higher than the synchronous speed. Three of the most common induction motors available are: 1) Shaded pole with a smaller fractional hp, with low torque; 2) Capacitor run and capacitor start motors, both requiring an additional capacitor to operate; 3) Three-phase motors which run on three phase supply voltage.
EC motors are Direct Current (DC) motors requiring no brushes. The stator has a set of fixed windings and the rotor contains permanent magnets. The phases in the stator's fixed windings are continually switched by a circuit board which keeps the motor rotating. Since it is the commutation electronics that control the speed of the motor, EC motors are not limited to synchronous speeds. In the past, the lower power output of DC and EC motors has restrained them to applications such as small fans, pumps, servomotors and motion control systems. However, advances in electronics and materials are allowing larger output motors, up to the 12 kW and higher. There are now virtually no restrictions for these motors that are now increasingly used in applications such as small appliances, electric vehicles and large rooftop condenser units.
The most common reason for choosing an EC motor over an AC motor is its efficiency. Since the commutation in an EC motor is provided electronically, it reduces the losses inherent to the AC motor.
An EC motor works differently from an AC motor. An EC motor contains a power supply and power driver to supply constant voltage sequenced with a precise timing through preferably three motor's wiring regardless of the AC input voltage.
The ability to control the speed of an EC motor permits a high level of efficiency. AC motors are available in various speeds and can also be controlled with external devices, but these can generate other problems such as noise and lack of optimization for the system. Variable Frequency Drives (VFDs) can control three-phase motors, but in order to properly protect the motor from damage, a complex system of filtering and protection is required.
Many EC motors offer Bus communication, such as Modbus. Two-way communication between a device and a motor, with information-rich feedback, is now available through Bus communication. For example, Bus communication can be easily integrated in building management systems where each motor can be referenced individually or in groups, and the status of individual fans can be seen and changed as needed.
In complicated control scenarios, it is now possible to include such features as loosening a blocked rotor by reversing rotation on start-up or loosen frozen fan blades using a soft start override. A default setting under Bus communication interruption can also be programmed for the electronics.
EC motors can also be used in multiple motor operation. For example, in multiple fan systems (rooftop condensers for instance), it is possible to have one fan as the master controlling all the other fans. Since the EC motor integrates all the necessary logic, a separate controller is no longer needed.